Vehicle power transmissions come in a variety of configurations, including automatic, manual, dual-clutch, and automated manual transmissions. The clutches of a typical automatic and manual/standard transmission are applied via clutch pistons, which are actuated using hydraulic fluid circulated at relatively low pressures. Due to the low pressure construction of automatic transmissions, hysteresis tends to be minimal. As a result, automatic transmissions are controlled primarily via pressure-based feedback control logic.
By way of contrast, a dual-clutch transmission (DCT) and an automated manual transmission (AMT), both of which combine certain features common to manual and automatic transmissions, operate at higher pressures. As a result, DCTs and AMTs are more prone to the effects of hysteresis. Such transmissions are therefore often controlled via position-based control logic, wherein a particular position is commanded and monitored for the clutch piston as opposed to a particular pressure. All of the transmissions described above may use variable force solenoid valves to control hydraulic pressure and flow to a given actuator.